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viral agents that cause infectious pharyngitis (strep throat)



bacterial agents that cause infectious pharyngitis (strep throat)

Strep pyogenes (usuallyGroupA β‐Strep)
Corynebacterium diphtheriae


signs and symptoms of strep throat/infectious pharyngitis

•Throat pain
•Difficulty swallowing
•Red and swollen tonsils, sometimes with white patches or streaks of pus
•Tiny red spots on the soft or hard palate — the area at the back of the roof of the mouth
•Swollen, tender lymph glands (nodes) in the neck
•Stomachache and sometimes vomiting, especially in younger children


why must you test specifically for strep throat to diagnose it

one can have all the signs and symptoms and not have a true strep throat infection -- more likely to get these symptoms from a viral infection or less likely from other illnesses


can you tell by looking into the mouth if the cause of an infectious pharyngitis is bacterial or viral

no you cannot tell by looking so one must do a point of care test to be sure


viral agents that cause bronchiolitis

Influenza Virus
Respiratory Syncitial Virus

think AIR through the bronchioles


bacterial agents that cause bronchiolitis

Bordetella pertussis
Mycoplasma pneumonia


what are the assays used for the microbial agents of bronchiolitis

you do a swab to use the assay

for the viral AIR agents
Adenovirus: PCR, antigen detection
Influenza virus: virus isolation
Respiratory syncitial virus: antigen detection

for the bacterial agents
bordatella pertussis: culture, DFA, serology, PCR
mycoplasma pneumonia: acid fast, culture


respiratory bacteria by definition have what type of oxygen requirements

aerobes and facultative anaerobes


how do you culture media for respiratory bacteria

get a routine sputum specimen and you can use either a blood, chocolate, or macconkeys agar


significance of using chocolate and mcconkey agar

chocolate agar - blood agar that has been heated to break open RBCs and release their content

mcconkeys: for selection and differentiation


what pathogens required special growth media that is not standard and what agar do they use

bordatella pertussis: bordet- gengou
c. diphtheria: tinsdale agar


characteristic of streptococci

small, gram positive, cocci in shape, metabolized through fermentation with lactic acid production, facultative anaerobe (but actually have all the qualities of aerotolerant anaerobe - grow in presence of oxygen, metabolize via fermentation, have only superoxide dismutase)


clinical syndrome of streptococci pyogenes

pharyngitis (strep throat)


describe the name streptococci pyogenes

Group A streptococcus according to Lancefield classification
pyogenes = induce of pus formation due to leukocidin production (leukocidin destroys leukocytes which will make pus)


how are streptococci classified

based on 16s rRNA sequencing


streptococci are classified by groups based on

polysaccharides (major cell wall carbs)
there's group A --> W though there is no I or J


example of streptococci that does not have a carb group

S. pnuemonia


lab identifications of streptococci

-􏰀Gram Positive Spheres in chains (Older cultures become Gram Variable)
-􏰀Lack catalase (facultative anaerobes)
-􏰀Growth enhanced by CO2
-􏰀Nutritionally fastidious (􏰀Normal culture medium = Blood agar (BA) 􏰀Yeast extract + peptone +5% blood)


streptococcal have large amounts of virulence factors which is not all expressed by all strain. what determines this variability?

transduction mediated gene transfer or transformation


describe s. pyogenes on blood agar

-where there is production of streptolysin S, there is beta hemolysis (tot destruction of erythrocytes) making the plate transparent
-sensitive to bacitrain so no growth where this antibiotic is present


clinical syndrome of corynebacterium diphtheria

severe pharyngitis (diphtheria)


physical features of corynebacterium diphtheria

gram positive, club shaped, nonsporeforming rods that are pleomorphic with chinese letter arrangement


what does corynebacterium diphtheria looks like on a gram stain

irregular in shape
rod shaped
one end is thicker than the other


why is corynebacterium diphtheria unusual in developed countries

because of DPT vaccine -- the D component is diphtheria toxoid


where are endemics and outbreaks of diphtheria seen

endemics - subtropical and tropical areas
outbreak - places with breakdown in health infrastructure


pathogenesis of corynebacterium diphtheria

organism is non invasive and does not enter the bloodstream but the toxin that it releases enters the blood stream and invades tissues

organism grows in a biofilm on the surface of the pharynx while its necrotizing toxin kills the tissue that it gets to


main virulence factor of diphtheria

the diphtheria exotoxin


how are the genes for diphtheria toxin acquired

via lysogenic conversion


complication of diphtheria

pharyngitis can be so severe that it blocks the airway --> suffocation

bull neck, pseudomembranous